An enterprise has employed an enterprise mobility system (EMS) because the EMS enables the enterprise to become a Real Time Enterprise (RTE) which decreases costs related to communication and respective communications, improves operational efficiency and processes all tasks in real time basically. The EMS is a system for allowing an enterprise to process tasks in real time at any time, and anywhere using mobile devices, mobile solutions, network communication networks or the like. In particular, a voice call service has been used using an Internet Protocol Private Branch eXchange (IP PBX).
On the other hand, the IP PBX uses an Add On Module (AOM). Various functions requested by a user, such as a Direct Station Select (DSS) function or a Busy Lamp Field (BLF) function, may be assigned to respective key buttons of the AOM and be used. The DSS function is a function for allowing a user to perform a call-forward to any extension by selecting one key, and the BLF function is a function for allowing a user to check the state of extensions that are busy using LEDs. For example, when an LED is turned off, a corresponding extension is in an idle state, and when an LED is flickering, or when the LED is turned on while ringing occurs, a corresponding extension is busy. Also, a user performs functions, such as a call transfer function, a call pick up function, call dialing or the like, using the AOM.
Also, the user may login to the EMS and indicate the user's own state in absence, busy, idle states or the like and use a presence function for enabling group users which are registered in real time to check the states thereof.
However, in prior art, when the IP PBX functions are applied to a smart phone, the states of group users (that is, the state information (for example, busy, incoming, idle or the like) of a terminal provided by the AOM) are continuously provided, battery consumption may increase. Further, the call states of the group users are only displayed, so that it is impossible to know the call states of other users besides the group users.
On the other hand, if the presence function is provided based on an existing server/client model, the state of a user is updated in real time and the user's presence is displayed on a background screen when the state of the user is changed, thus increasing battery consumption and, also, causing a user to update the user's own state.